Heat-bondable fibers



United States Patent 3,537,880 HEAT-BONDABLE FIBERS Joseph M. Kuzmak, Media, Pa., assignor to FMC Corporation, Philadelphia, Pa. a corporation of Delaware No Drawing. Filed Jan. 31, 1967, Ser. No. 612,809 Int. Cl. B44d 1 44; B32b 23/08 U.S. Cl. 117-621 3 Claims ABSTRACT OF THE DISCLOSURE Rayon fibers rendered heat-bondable by providing the same with an ultra-thin surface film of nylon by interfacial polymerization which involves applying onto preformed rayon staple fibers a solvent solution of orthophthaloyl chloride, isophthaloyl chloride and sebacoyl chloride and thereafter reacting such solvent solution with an aqeuous solution of hexamethylenediamine.

The present invention relates to a method of making heat-bondable rayon staple fibers.

In the art of producing woven and non-woven fabrics or textiles, it is known that non-thermoplastic fibers, such as rayon fibers, may be intermixed with thermoplastic materials, deposited as a mat or formed into yarns and then bonded under heat and pressure. It is also known that in non-woven fabric manufacture, non-thermoplastic fibers alone may be deposited as a mat, then treated in situ with thermoplastic or thermosetting resins and fiinally bonded under heat and pressure.

While satisfactory to some degree these and other similar known procedures lack flexibility, often result in non-uniform and marginal fiber bonding and, to some extent, involve Waste of materials. Attempts to provide non-thermoplastic staple fibers, such as of rayon, with some type of heat-sensitive coating, which could be activated when desired, have been unsatisfactory. In some instances, the thermoplastic material which was intended to serve as a surface coating penetrated into the fibers so that little or no fiber bonding could be achieved. In other instances, if fiber bonding was possible, the fibers either cemented to each other or experienced considerable dusting when subjected to conventional textile operations, such as carding, combing, drafting, spinning and weaving. Accordingly, a primary object is to provide new or generally improved or more satisfactory method for making heat-bondable rayon staple fibers.

Another object of this invention is the provision of a method for making heat-bondable rayon staple fibers which are capable of being processed by conventional textile fiber methods without loss or sacrifice in their heatbondable characteristics.

Still another object is the provision of a method of making modified rayon staple fibers which can be bonded by heat alone or both heat and pressure under conditions which do not damage the physical properties or appearance of the fibers themselves.

A further object is to provide a method for rendering rayon staple fibers heat-bondable which is simple, reliable, and economical.

These and other objects are accomplished with this invention by depositing on the surface of rayon staple fibers, by interfacial polymerization, an ultra-thin film of polyamide having a melting temperature of from about 130 to 180 C. The amount of polyamide deposited on the rayon fibers can vary with the degree of bonding desired. Based upon the weight of the rayon fibers, polyamide deposition or add-on levels of from about 2 to 4% provide for a light to medium, but satisfactory fiber bonding. An ad-on level of polyamide of about 6% results in very good fiber bonding and is generally satisfactory ice for most non-woven fabric applications, while the use of from 8 to 9% or more of polyamide provides for excellent fiber bonding and would be employed in making non-woven fabrics which might be subjected to more rugged handling and/ or use than conventional non-woven fabrics.

The interfacial polycondensation method of preparing the heat-bondable rayon staple fibers involves, essentially, reacting hexamethylenediamine in an aqueous phase with organic acid chlorides dissolved in an organic solvent. The aqueous phase includes, besides the diamine, sodium carbonate which serves to neutralize hydrochloric acid formed during the polymerization reaction, a wetting agent, such as Triton X100, an alkyl aryl polyether alcohol, which is a product of Rohm & Haas Company, Philadelphia, Pa., to provide for rapid spreading of the aqueous liquid, and a silicone emulsion, such as LE48, product of Union Carbide Corporation, to improve the hand of a resulting heat-bondable fiber.

More particularly, the rayon staple fibers are initially immersed in the solvent solution of the organic acid chlorides. Wetting out of the rayon fibers in this solution occurs rapidly and thus the duration of the immersion can be very short, with an immersion of from less than 1 minute to about 5 minutes usually being satisfactory. To insure good penetration, the staple fibers are preferably opened prior to immersion by a conventional staple fibers preopening apparatus, such as pickers.

Rayon fibers thus treated are then centrifuged to reduce the pick-up of the solvent solution to about 50% or slightly less, based upon the weight of the fibers. During such extraction, care must be exercised to minimize the formation of liquid lenses, particularly in those portions of the fibers directly adjacent to the centrifuge wall. Of importance, I have found that only centrifugation has proved effective in reducing the solvent solution pick-up to the above-mentioned limit. Solvent solution retention by the fibers of substantially more than 50% generally results in spotty and heavy deposits of polymer, with some ce-mentation of the fibers, and should therefore be avoided. Squeezing of the solvent solution from the rayon fibers by means of an ordinary wringer is unsatisfactory, because of the high stiffness of the fibers, and generally leaves as much as 200% of the solvent solution remaining on the fibers. Some improvement over a conventional wringer is achieved by suction of the solvent solution from the treated fibers through filter paper, but this procedure also fails to reduce the pick-up of the solvent solution to low enough levels. Whether the rayon staple fiber is oven-dried or not before immersion in the solvent solution has little effect upon the hydrolysis of the acid chlorides.

Once the desired amount of solvent solution has been provided on the rayon staple fibers, the fibers are immediately immersed in the aqueous phase to minimize hydrolysis of the acid chlorides. The presence of the wetting agent in the aqueous phase, facilitates rapid and thorough wetting of the mass of fibers, although a slight working of the fibrous mass is preferred to encourage such penetration.

The polyamide forms as a film almost instantaneously at the interface of the contact of the two phases; namely, the solvent solution retained on the surface of the rayon staple fibers and the aqueous phase in which the fibers are immersed. The duration of immersion of the fibers in the aqueous phase may be varied and, in general, will not exceed perhaps 10 to 15 mniutes.

Following the deposition of the polyamide onto the fibers, excess aqueous solution is removed, as by squeezing with a wringer, after which the fibers are thoroughly washed with water and dried at a temperature of about 3 70 to 75 C. Microscopic examination of the resulting heat-bendable rayon staple fibers have established that the polyamide is formed as a continuous film or coating on the surface of the fibers.

It is critical in the production of satisfactory heatbondable rayon staple fibers that the steps of the method be performed in the order as described above, with the fibers being immersed in the aqueous solution after the desired level of solvent solution has been applied thereto. Reversing the order of these steps from that described above does result in a deposition of polyamide coatings on the surfaces of the rayon staple fibers. However, such coated fibers tend to cement to each other when undergoing conventional textile processing and thus are unsatisfactory. Moreover, when such fibers are subjected to heat, as during bonding, the fibers become yellow and are therefore unsuitable from the standpoint of appearance. A still further objection, which arises when the aqueous solution is first applied to the fibers, is that the water carried into the solvent solution results in rapid hydrolysis of the acid chlorides.

Of still further importance in the practice of the present invention is that the polyamide which is deposited onto the rayon staple fibers have a melting temperature preferably within the range of from about 130 to 180 C. A polyamide coating softening within such range permits the resulting coated fibers to be bonded at temperatures which would neither damage nor destroy the physical properties or appearance of the fibers and would enable the finished bonded textile fabrics to withstand the elevated temperature to which such fabric would normally be subjected.

Nylon 6,6 and nylon 6,10, as such, are both unsatisfactory in view of their reported high melting points of 268 C. and 210 C., respectively. In accordance with this invention, however, heat-bendable rayon staple fibers having a polyamide coating which melts within the desired range of from 130 to 180 C. and which does not dust or cement when subjected to normal textile processing operations is produced by employing a solvent solution containing a combination of orthophthaloyl chloride, isophthaloyl chloride, and sebacoyl chloride.

It is important in the practice of the present invention that all three of the mentioned acid chlorides be employed in combination since the absence of any one of such chlorides results in fibers which are heat-bondable but unsatisfactory for commercial use. A solvent solution of sebacoyl chloride alone results in deposition of a polyamide which is beyond the desired softening range and tends to dust. On the other hand, a solvent solution containing orthophthaloyl chloride provides for polyamide coatings on rayon staple fibers which will melt at about 150 C., well within the desired range. Such coatings, however, undergo considerable dusting when the fibers are subjected to conventional textile processing operations, as for example carding. Some reduction in dusting has been achieved by employing a terpolymer of orthophthaloyl chloride, but the degree of dusting which remains still renders such heat-bondable fibers unsatisfactory for commercial use.

The use of isophthaloyl chloride in the solvent solution is also capable in forming polyamide coatings on the fibers. In this instance, the coatings do not dust but do cement the fibers when they are subjected to conventional textile operations. Moreover, this latter objection is neither eliminated nor lessened when a solvent solution of isophthaloyl chloride is modified by the addition of orthophthaloyl chloride.

The ratio of orthophthaloyl chloride, isophthaloyl chloride and sebacoyl chloride employed in the solvent solution can, of course, be varied. The proportions of these different chlorides are based upon the particular properties desired in the polyamide coating which is to be deposited on the fibers, with generally the orthophthaloyl chloride controlling the melting point of the coating, whil the isophthaloyl chloride and the sebacoyl chloride rendering the resulting coating resistant to dusting and premature cementation.

As heretofore mentioned, the amount of polyamide added onto the rayon staple fibers can be controlled, to suit the particular need for which such fibers are intended, by varying the concentrations of the solvent and aqueous phase solutions.

The heat-bondable rayon staple fibers produced by the method of the present invention retain their original free or separated and open characteristics until intentionally activated. They can be stored, transported and handled with little risk of fiber cementation. These staple fibers may be worked in a textile operation or dispersed as a mat and, when subjected to a temperature above the softening point of the applied polyamide, will bond to each other. If one desires stronger interfiber bonding or an article of a specified shape, pressure may be applied to the article along with heat to obtain the desired result.

Of significance is that the heat-bondable rayon fibers formed by the method of the present invention exhibit far better interfiber bonding when in a moist condition at the time of heat application. For example, heat-bondable rayon fibers prepared by the method of the present invention, which normally exhibited good bonding properties after the polyamide coating was applied thereto, could not be bonded under heat or heat and pressure after being dried in an oven at 105 C. Remoistening of such dried fibers with either steam or by wetting out in water, restored to such fibers their intended heat-bendable characteristic. Moreover, huch moistened fibers exhibited better bonding tendencies than fibers which were merely in equilibrium with the moisture in the atmosphere.

The following example is set forth to demonstrate the method of this invention and the properties of the resulting heat-bondable fibers.

Solvent and aqueous solutions were first prepared as follows:

SOLVENT SOLUTION Mls, Isophthaloyl chloride 1.4 Sebacoyl chloride 5.4 orthophthaloyl chloride 20.2 Stoddard solvent (white spirits) 200.0

AQUEOUS SOLUTION 70% solution of hexamethylenediamine mls 27.0 Sodium carbonate gms 8.0 Silicone LE48 mls 2.0 Triton X gm 0.5 Water mls 200.0

A mass of conventional rayon staple fibers, 1% length and 1.5 d./f., was preopened by a picker, and immersed first in the above-noted solvent solution for a period of 2 minutes. This treated mass was then centriuged to reduce the solvent pick to about 50%, with the centrifuge wall lined with absorbent paper to minimize the formation of liquid lenses in the portion of the staple fibers directly adjacent thereto.

The staple fibers were then immediately immersed in the aqueous solution and were worked slightly to aid penetration. Almost instantaneously, upon immersion, the polyamide formed as a film at the interface of contact of the two solutions.

After a 10 minute soaking, the staple fibers were removed, squeezed with a wringer, Washed thoroughly with water and dried at 75 C.

The add-on level of polyamide obtained Was between 8% and 9% and the now heat-bondable rayon staple fibers were found to be non-dusting and filament-free; that is, no fiber cementation. Analysis of the polymer which had formed indicated that it had a melting point of 158 C. and started decomposing at 225 C.

The heat-bondable rayon staple fibers were deposited as a mat and then bonded using heat as follows:

160-l70 C. for secondsgood bond 160170 C. for 60 seconds-bond destroyed 230245 C. for 3 secondsgood bond 230245 C. for 10 seconds--bond destroyed Tests of the resulting non-woven fabrics indicated that, in general, the bond realized with the higher temperatures and shorter application periods provided fabrics which were somewhat stronger than those obtained when lower temperatures were employed. The above data also established that, even at temperatures below the decomposition temperature of the polymer, bond destruction was experienced, apparently due to the polymer melting away from the fibers during the longer heat application periods.

A mass of the heat-bondable rayon staple fibers, prepared as described above, were dried in an oven at 105 C. and immediately thereafter tested for bonding. However, no bond could be obtained. When such fibers were remoistened with steam or wet-out in water, they once again bonded very well and better than fibers of the same type which were merely in equilibrium with the moisture in the atmosphere.

It is to be understood that changes and variations may be made without departing from the spirit and scope of the invention as defined in the appended claims.

I claim:

1. A method of making heat-bondable rayon staple fibers by forming on the surfaces of preformed rayon staple fibers a substantially non-dusting coating of a polyamide having a melting point within the range of from 130 to 180 C. which includes the steps of first applying onto preformed rayon staple fibers a solvent solution of isophthaloyl chloride, sebacoyl chloride and a major portion of orthophthaloyl chloride, removing excess solvent solution from such staple fibers, immediately thereafter reacting the acid chlorides remaining on the staple fibers with an aqueous solution of hexamethylenediamine whereby polyamide films are formed at the interface of acid chlorides remaining on the staple fibers and the aqueous solution, washing the now surface coated staple fibers to remove the exess aqueous solution, and there after drying the coated staple fibers.

2. A method as defined in claim 1 wherein the rayon staple fibers are sequentially immersed in both of said solutions and are centrifuged after immersion in the solvent solution to reduce solvent solution retention by the fibers to not more than based upon the weight of the fibers.

3. A method as defined in claim 1 wherein the polyamide coated rayon staple fibers are washed with water and dried by heat at a temperature of from to C.

References Cited UNITED STATES PATENTS 2,191,556 2/1940 CarOthers.

2,252,554 8/1941 Carothers.

2,610,927 9/ 195.2 Foulds 117145 X 2,882,185 4/1959 Vallco et a1.

2,957,783 10/1960 Dachs et a1. 117-161 X 3,198,771 8/1965 Gabler 117161 X 3,227,579 1/1966 Bluestein 117--l45 X 3,332,907 7/1967 Angelo et al 117-161 X 3,418,275 12/1968 Stephens 117-16 1 X 3,078,138 2/1963 Miller et al. 117-141 X 3,383,162 5/1968 Whitfield et al. 1l7-141 X FOREIGN PATENTS 1,022,151 3/1966 Great Britain.

WILLIAM D. MARTIN, Primary Examiner M. L. LUSIGNAN, Assistant Examiner US. Cl. X.R.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION 3,537,880 Dated November 3, 1970 Patent No.

Inventor(s) K Joseph It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In the title, insert "METHOD OF MAKING" before HEATBONDABLE FIBERS-; C01. 1, line 5 4, "of" (second occurrence) should be "for".

SIGN ED mu SEALED W2 19" Amen mm mm a.

Oomissioner or Patents FORM PC40 USCOMM-DC scan-Poo 

